The Cassegrain design is a type of telescope that uses a combination of mirrors to focus light. It features a primary mirror that collects light and a secondary mirror that reflects it back through a hole in the primary mirror. This design allows for a compact telescope structure while maintaining a long focal length, making it ideal for astronomical observations. Cassegrain telescopes are popular among both amateur and professional astronomers. They can be used for various applications, including planetary observation and deep-sky imaging. The design is named after the French astronomer Laurent Cassegrain, who developed it in the 17th century.